Polyvinyl alcohol stabilized aqueous emulsions containing ethylene-vinyl chloride (EVCl) copolymers are commonly used as film formers or binders for coating, adhesive and saturation applications. However, substrates impregnated with such emulsions typically experience a measurable loss in structural integrity when exposed to nonaqueous solvents such as methyl ethyl ketone, mineral spirits and the like. Numerous formulations have been developed in an effort to overcome the diminished solvent resistance exhibited by substrates impregnated with these emulsions.
U.S. Pat. No. 3,501,440 discloses the copolymerization of vinyl chloride and ethylene and other copolymerizable monomers including methyl acrylate and butyl acrylate in the presence of a free radical catalyst. Reference examples 5-6 teach the use of polyvinyl alcohol as a suspending agent in the copolymerization of ethylene and vinyl chloride.
U.S. Pat. No. 3,895,167 discloses a metal coating composition comprising a vinyl chloride-ethylene copolymer and a heat curable, thermosetting aminoplast resin mixture of a methylolated ethyleneurea resin and an alkylated triazine/formaldehyde condensate. The vinyl chloride-ethylene copolymer compositions must necessarily be prepared from a mixture of the methylolated ethyleneurea resin and the condensate. Omission of either of these aminoplast resins from the copolymer recipe renders the composition unsuitable for metal coating applications.
U.S. Pat. No. 4,189,415 discloses an aqueous emulsion containing a vinyl chloride-vinyl acetate-ethylene copolymer and polyvinyl alcohol as the sole protective colloid. Depending upon the desired application, from 0.5 to 5 wt % of an olefinically unsaturated N-methylolamide such as N-methylolacrylamide is added to the polymer premix.
U.S. Pat. No. 4,528,315 discloses a process for preparing aqueous copolymer emulsions of vinyl halides and/or vinyl esters and additional monomers in the absence of emulsifying agents. Example 9 teaches a vinyl chloride-vinyl acetate-ethylene copolymer also containing hydroxypropyl acrylate, acrylamide and acrylic acid.
U.S. Pat. No. 4,623,462 discloses a filter substrate which is impregnated with a water-based binder comprising a latex containing at least 20 wt % polymerized vinyl chloride in the latex solids. The latex is an aqueous emulsion containing a copolymer of vinyl chloride, 30 to 60 wt % lower alkyl acrylate and one or more comonomers selected from acrylic acid and N-methylol acrylamide. Such comonomers may be added to the polymer premix in an amount up to 5 wt % based on the total weight of the monomers. The binder also contains 5 to 20 wt % of a crosslinking resin based upon the weight of the latex solids.
U.S. Pat. Nos. 4,673,702, 4,714,731 and 4,716,192 disclose polyvinyl alcohol-stabilized vinyl chloride-ethylene copolymer emulsions as coatings for metal substrates. Such emulsions comprise from 20 to 70 wt % of a copolymer colloidally dispersed in an aqueous medium, the copolymer comprising 65 to 90 wt % vinyl chloride, 5 to 35 wt % ethylene and 0 to 10 wt % olefinically unsaturated copolymerizable monomer. Suitable copolymerizable monomers include N-isobutoxymethylacrylamide and N-methylolacrylamide.